Google Drive and all its components: I cannot say enough good things about Docs, Slides, Sheets, and Forms...the possibilities are endless!

Google Earth Voyages: fantastic for virtual field trips or to just add a little extra "oomph" to your lesson

Google Hangouts: Conduct meetings even when you're not in the same room! I love the "share my screen" feature, which allows me to let teachers see what my screen looks like as I walk them through a project

Google Voice: gives you an extra phone number that connects to your existing mobile number. Great for making parent phone calls or texts without revealing your personal phone number.

Sign Up Genius: I used this when I taught Science Lab to gather volunteers for stations during Science Night. Since then, I've seen it used for potluck lunches, field trip volunteers, and mystery reading guest sign-ups.

Socrative: a digital assignment tool where any amount of planning will work

Symbaloo: Out of all the ways to share links with students, this one is probably the easiest and most universal.

TweetDeck: schedule your tweets in advance and keep up with Twitter chats more easily

Wifi Mouse: an iOS app that works over Wifi to connect to your computer and act as a mouse, letting you control your computer screen from anywhere in the room